an introduction to the vodafone gprs · pdf file1.1 etsi gsm technical specifications ... bss...

This document is issued by Vodafone Ltd. (Herein referred to as Vodafone) in confidence and is not to be reproduced inwhole or in part without the prior written permission of Vodafone. The information contained herein is the property ofVodafone Ltd. and is to be used only for the purpose for which it was submitted. It is not to be released in whole or in partwithout the prior written permission of Vodafone Ltd. Some text is reproduced herein from ETSI GSM specifications with thekind permission of ETSI.

© Vodafone Ltd., 2000

The Courtyard

2-4 London Road

Newbury

Berkshire

RG14 1JX

AN INTRODUCTION TO THEVODAFONE GPRS ENVIRONMENT

AND SUPPORTED SERVICES

Issue 1.1/1200December 2000

Amendment Record

Issue Date Comments

Draft A 31/07/2000 Draft for review, ND

Draft A1 01/08/2000 Changes identified by NP and AC incorporated by ND.

Draft A2 01/08/2000 Changes to section on ‘Bandwidth’

Draft A3 14/08/2000 Added two new appendices; ‘Throughput Calculations’ and ‘GPRS NetworkArchitecture.’

Corrected +CGREG to +CGREQ in Mitsubishi example.

Issue 1.0 23/08/2000 Added appendix describing GPRS Connection Script. Raised to issue level, ND.

Issue 1.1 17/12/2000 Updated for new handsets and software, NP

Additions made for Motorola T260 and Ericsson R520 handsets

Modified to include Wireless Login Client software

Additional information about development area LAN configuration and facilities

References

[No.] Document Name Issue

1 GSM 02.60: “Digital Cellular Communications System (Phase 2+); GeneralPacket Radio Service (GPRS); Service Description, Stage 1”

V8.1.0 1999

2 GSM 03.60: “Digital Cellular Communications System (Phase 2+); GeneralPacket Radio Service (GPRS); Service Description, Stage 2”

V6.7.0 1997

3 GSM 07.60: “Digital Cellular Communications System (Phase 2+); GeneralPacket Radio Service (GPRS); Mobile Station Supporting GPRS”

V6.5.0 1997

4 GSM 07.07: “Digital Cellular Communications System (Phase 2+); AT commandset for GSM Mobile Equipment (ME)”

V7.3.0 1998

AN INTRODUCTION TO THE VODAFONE GPRS ENVIRONMENT AND SUPPORTED SERVICES

Issue 1.1/1200 Page iii

Table Of Contents1. INTRODUCTION ...............................................................................................................................................................1

1.1 ETSI GSM TECHNICAL SPECIFICATIONS................................................................................................................11.2 GPRS MS FUNCTIONALITY........................................................................................................................................21.3 MODES OF CONNECTIVITY.......................................................................................................................................21.4 THE PDP CONTEXT.....................................................................................................................................................31.5 MOBILE TERMINATED GPRS DATA..........................................................................................................................31.6 GPRS BANDWIDTH AND THROUGHPUT..................................................................................................................41.7 WHAT ABOUT WAP? ...................................................................................................................................................4

2. GETTING STARTED.........................................................................................................................................................52.1 CAVEATS......................................................................................................................................................................62.2 PRELIMINARY SETUP.................................................................................................................................................62.3 CONNECTING WITH REFLECTION AND DIAL-UP NETWORKING..........................................................................6

2.3.1 GPRS Attach and Context Activation..................................................................................................................62.3.2 Dial-Up Networking ..............................................................................................................................................72.3.3 Ending The Session.............................................................................................................................................8

2.4 CONNECTING WITH VODAFONE’S WIRELESS LOGIN CLIENT.............................................................................82.5 TESTING THE IP LINK .................................................................................................................................................8

3. IP OVER PPP ....................................................................................................................................................................93.1 ESTABLISHMENT SEQUENCE...................................................................................................................................9

4. AT COMMANDS FOR GPRS..........................................................................................................................................104.1 INFORMATIVE EXAMPLES.......................................................................................................................................10

4.1.1 Querying the GPRS Device ...............................................................................................................................104.1.2 Mobile Initiated Context Activation.....................................................................................................................104.1.3 Entering the Data State......................................................................................................................................114.1.4 Abnormal Call Clear...........................................................................................................................................12

5. APPENDIX 1 – CONFIGURATION SETTINGS..............................................................................................................135.1 MODEM AND DIAL-UP NETWORKING SETTINGS..................................................................................................135.2 REFLECTION SESSION CONFIGURATIONS...........................................................................................................14

5.2.1 Custom Toolbar..................................................................................................................................................145.2.2 Macro Contents..................................................................................................................................................15

6. APPENDIX 2 - CONFIGURATION FOR VODAFONE GPRS CONNECTION SCRIPT ................................................166.1 HOW TO USE..............................................................................................................................................................166.2 LOCATION OF THE FILES.........................................................................................................................................166.3 SHORTCUT ON THE DESKTOP................................................................................................................................166.4 PROGRESS INDICATIONS AND SCRIPT BEHAVIOUR ..........................................................................................166.5 THE CONFIGURATION FILE .....................................................................................................................................17

6.5.1 Resetting The Config File...................................................................................................................................176.5.2 Manual Modifications.........................................................................................................................................18

6.6 FLOWCHART..............................................................................................................................................................186.7 HANDSET DEFINITIONS ...........................................................................................................................................19

6.7.1 Adding A New Handset......................................................................................................................................197. APPENDIX 3 – GPRS SPECIFIC AT COMMANDS .......................................................................................................21

7.1 GPRS AT COMMANDS ..............................................................................................................................................218. APPENDIX 4 – THROUGHPUT CALCULATIONS.........................................................................................................22

8.1 GSM AND THE AIR INTERFACE...............................................................................................................................228.2 GPRS DATA................................................................................................................................................................228.3 GPRS DATA CODING EXAMPLE..............................................................................................................................23

9. APPENDIX 5 – GPRS NETWORK ARCHITECTURE....................................................................................................259.1 THE GPRS NETWORK...............................................................................................................................................259.2 PROTOCOLS IN THE TRANSMISSION PLANE .......................................................................................................25

List Of Tables and FiguresTable 1 - GPRS MS Class Descriptions ........................................................................................................................................2Table 2 - Full List of GPRS PDP Types.........................................................................................................................................3Table 3 - Full List of Layer 2 Protocols ..........................................................................................................................................3Table 4 - Throughput Capabilities of GPRS ..................................................................................................................................4Table 5 - Modem and Dial-Up Networking Configuration Settings..............................................................................................13Table 6 - Custom Toolbar Objects in Reflection..........................................................................................................................14


Issue 1.1/1200 Page iv

Table 7 - Summary of AT Commands for GPRS.........................................................................................................................21Table 8 - Summary of Existing GSM AT Commands with GPRS Extensions............................................................................21Table 9 - Summary of AT Commands for GPRS Modem Compatibility Mode ...........................................................................21Table 10 - RLC Data Unit Capacity Per Radio-Block for CS1 to CS4.........................................................................................22Table 11 - Derivation of Data Rates Per Timeslot for Each Coding Scheme .............................................................................23Table 12 - Protocol Overheads Added to User Data ...................................................................................................................23Table 13 - Number of Radio-Blocks Required for a 1000 Byte Sample of Data .........................................................................23

Figure 1 - The Vodafone GPRS Development Environment.........................................................................................................5Figure 2 - Protocol Stack for IP Based Services...........................................................................................................................9Figure 5 - Flowchart for GPRS Connection Script.......................................................................................................................18Figure 3 - The Basic GPRS Network...........................................................................................................................................25Figure 4 - GPRS Transmission Plane..........................................................................................................................................26

Abbreviations

APN Access Point Namebps Bits per second (Not bytes). Often measured as multiples of 1024, i.e. Kbps.BSC Base Station ControllerBSS Base Station System (BTS+BSC+PCU)BTS Base Transceiver SystemCGSN Combined GPRS Support Node (SGSN+GGSN)GGSN Gateway GPRS Support NodeGPRS General Packet Radio ServiceGSM Global System for MobilityGTP Gateway Tunnelling ProtocolHLR Home Location RegisterIP Internet ProtocolKbps See bps.L2P Layer 2 ProtocolLLC Logical Link ControlMAC Medium Access ControlME Mobile EquipmentMO Mobile OriginateMS Mobile StationMT Mobile TerminatePAD Packet Assembler/DisassemblerPCU Packet Control UnitPDN Packet Data NetworkPDP Packet Data Protocol, e.g. IP, X.25PLMN Public Land Mobile Network, i.e. a mobile telephone operator.PSTN Public Switched Telephone Network, i.e. a fixed line telephone operator.QoS Quality of ServiceRLC Radio Link ControlSNDCP Subnetwork Dependent Convergence ProtocolSMS Short Message ServiceSMSC Short Message Service CentreTA Terminal AdapterTCP Transmission Control ProtocolTE Terminal EquipmentUDP User Datagram ProtocolV.250 ITU-T Specification, formally known as V.25ter


Issue 1.1/1200 Page 1

GPRS is a communications bearer service. This means nothing more than that it is a different underlying method formanaging the end-to-end transfer of data, where one or both ends are GPRS compatible Mobile Stations (MS).There are, however, some limitations regarding Mobile Terminated (MT) data that are discussed later.

GPRS is particularly suited to bursty traffic, as experienced when browsing the Internet and synchronising E-mail witha remote server. It is not suited for voice calls, where there is continuous traffic. The pros and cons of packetswitched methods vs. circuit switched methods are not discussed here.

Browsing the Internet typically consists of periods of data transfer interspersed with long periods of inactivity. Thepacket nature of GPRS is what allows the service to utilise the air bandwidth in a more efficient manner than GSMand to allow the bandwidth to be shared with other users.

GPRS connectivity is provided by a ‘context’, which is specified at the Packet Data Protocol (PDP) layer. TheInternet is a Packet Data Network (PDN) with IP as its PDP and is the first type of PDN to be supported by GPRS.

The Terminal Equipment (TE, i.e. software on a computer) must be able to manipulate the various transport layerprotocols, such as TCP and UDP. This guide describes both the AT commands used to control a typical GPRSdevice when in command mode and the use of utilities that already know how to deal with TCP/UDP packets, suchas Dial-Up Networking in Microsoft Windows.

This document is intended to provide an overview of the new functionality that has been defined by ETSI for use withGPRS compatible Mobile Equipment. It focuses on the interface between the Terminal Equipment and the network,providing examples appropriate to the Vodafone GPRS test network.

Three particular GPRS handsets are dealt with here, the Ericsson R520 prototype, the Motorola T260 and theMitsubishi Trium, with the emphasis being on the first two. In discussing the setting up of a GPRS connection, somebackground knowledge of serial communications, AT commands and Windows communications is assumed.

1.1 ETSI GSM Technical Specifications

Detailed descriptions of the service can be found in ETSI GSM 02.60[1] and GSM 03.60[2].

The MS operation, such as PDP context activation and interfacing to external PDNs as described in GSM 07.60[3] iscovered here.

The AT commands defined for the service are introduced, although this reference is not intended to provide adetailed guide of the syntax and responses for every command. The full list of cellular AT commands and theirsyntaxes can be found in ETSI GSM 07.07[4].

Extracts from some of the ETSI documents listed in the References section are used here with permission. Originaldocuments are available from

ETSI650 Route des Lucioles F-06291Sophia AntipolisCEDEXFrance

Tel: +33 492 844200Fax: +33 493 654716E-mail: [email protected]: www.etsi.org

1. INTRODUCTION



1.2 GPRS MS Functionality

ETSI have defined three classes for GPRS MS functionality. Class-A supports simultaneous GPRS and GSM traffic,Class-B supports switching circuits between the two while Class-C supports operation in only one mode at a time.

Table 1 - GPRS MS Class Descriptions

Handset Class Functionality

A GPRS and GSM simultaneously

B Either of GPRS or GSM at any given time

C GPRS or GSM exclusively

CG Class-C in GPRS only mode

CC Class-C in circuit switched only mode (lowest mode)

Class-A handsets will be able to support simultaneous attach, activation, monitoring, invocation and data transfer inboth GPRS and GSM modes. Calls can be made or received on both services subject to the QoS parameters.

Class-B will be able to attach to, activate and monitor both services simultaneously but only be able to support datatransfer on one at a time. Active GPRS virtual circuits are not cleared down when GSM facilities are in use, but anyattempt to contact the PDP address will result in a “busy or held” indication. For instance, if an incoming GSM call isanswered, the GPRS connection is put on hold. This may cause problems for some applications using the GPRSconnection, e.g. a file transfer may be aborted because the transfer protocol timeout expired.

It is anticipated that some Class-B devices will be available in time for the launch of the service. Class-A handsetswill be available at a later date.

Class-C handsets will only be able to operate exclusively in one mode at a time, i.e. non-simultaneous attaches.Manually changing from one mode to the other involves detachment from the previously selected service.

The AT command AT+CGCLASS will indicate the current mode and which modes are supported.

The range of PDPs and L2Ps supported by a given handset is independent of the class of the device, although it isenvisaged that the more sophisticated the class, the more PDPs may be supported, e.g. X.25 in addition to IP.Availability of services at the handset is also dependent upon the services offered by the network and Vodafone haveno plans, at present, to support services other than IP.

1.3 Modes of Connectivity

A conventional GSM device is either switched on or it is switched off. When it is on, it is attached to the network andthe HLR tracks the device to know which Base Station it is registered on.

When in a call, a conventional GSM device maintains a dedicated circuit from endpoint to endpoint. The MS is thesole user of one single timeslot across the air interface and a circuit switched connection is set up through thenetwork, which again, is not shared with any other party. Even when no data is being transmitted, the resources arestill consumed whilst in the call.

GPRS is an extension of GSM. Therefore the MS is registered with the network in a similar way and the networktracks the location of it so that it knows where data packets should be sent. An Attach is made with the SGSN ratherthan the HLR and the serving GPRS cell is tracked.

For devices capable of supporting simultaneous GSM and GPRS attach (Class-A and Class-B), the device may beregistered on different cells for GSM and GPRS as it sees fit.

An attached GPRS device may activate one or more contexts. When a context is active, the device is assigned aPDP Address (which may have been specified by the device, i.e. static IP addressing), so that devices on the sameor other connected networks may reach it. The host of the PDN provisions dynamic IP addresses, so that the GPRSMS looks like any other device physically located on that network.

The GPRS test network only supports static IP addressing at present. Each developer will be informed of the IPaddress associated with the handset that they are using. Dynamic addressing will be introduced early on during thetrials.



When an attached GPRS device sends or receives data it makes use of shared network resources. Unlikeconventional GSM, it is not the sole user of the radio channel or of any other network resource. A virtual circuit isestablished for each communication. This means that although the channel has the appearance of an end-to-enddata pipe, individual data packets may take very different routes through the network.

1.4 The PDP Context

The Mobile Station establishes a context when it decides it requires a presence on a Packet Data Network. If a MSdoes not have an active context, it cannot be contacted at all via the GPRS network.

When attached, a GPRS device can send and receive data packets just like any other IP device. In fact, the GPRSstandard allows the MS to specify the PDP (Packet Data Protocol) and even the layer two protocol (L2P) to use.GSM 07.07 lists the following PDP and L2P values;

Table 2 - Full List of GPRS PDP Types

PDP Type

IP Internet Protocol (IETF STD 5)

OSPIH Internet Hosted Octet Stream Protocol

X25 ITU-T/CCITT X.25 layer 3

PPP Point to Point Protocol (IETF STD 51)

Table 3 - Full List of Layer 2 Protocols

Layer 2 Protocols

NULL None, for PDP type OSP:IHOSS

PPP Point-to-point protocol for a PDP such as IP

PAD Character stream for X.25 character (triple X PAD) mode

X25 X.25 L2 (LAPB) for X.25 packet mode

M-xxxx Manufacturer-specific protocol (xxxx is an alphanumeric string)

Please consult manufacturer specific documentation to determine the range of protocols supported by an individualdevice.

1.5 Mobile Terminated GPRS Data

Data can only be received at a GPRS device if the device is attached to the service and has an active context in anaccessible address space. Under such conditions, IP packets can be sent to the mobile as if it were any other deviceon the IP network. It is then up to the application to decide what to do with the incoming data.

A context can only be activated by the mobile station. If the GPRS device does not have an active context, andtherefore no PDP address, alternative methods of communicating with it must be considered.

It is generally recommended (a recommendation that extends to circuit switched GSM too) that Mobile Originated(MO) calls are preferred to Mobile Terminated (MT) ones. Statistics show that call success rates are far higher forMO than MT and some of the reasons include the fact that the Mobile Station may be busy, switched off or out ofcoverage at the time when the calling party is trying to reach it.

Many mobile applications involve a fixed or static host that is typically available. Therefore the mobile is more likelyto reach the host at any given time, provided enough circuits are available, than vice-versa.

Network initiated context activation will not be possible within GPRS for some time. The device has no PDP addressand so the GPRS network cannot reach it. There are currently no other GPRS specific methods by which the devicecan be contacted.



For Class-A and Class-B GPRS devices it may be possible to make a mobile terminate GSM transmission (a datacall or an SMS) to request that the device activate a context and issue a reply to the remote party. This is a perfectlyacceptable scenario, subject to the conditions of those classes.

A Class-C device that only supports GPRS, or that is not currently operating in GSM mode will not be able to accepta MT GSM call and so cannot be requested to attach in this way. If a Class-C device can support both GSM andGPRS modes then it is advised that the device remain in GSM mode when not active on the GPRS service.

1.6 GPRS Bandwidth and Throughput

The bandwidth available to the GPRS user is dependant upon several factors. In order to increase the bandwidth perchannel, a different Coding Scheme can be chosen, but this is at the expense of reduced error protection

ETSI have defined four coding schemes, from CS1 (highest error correction, lowest data rate) to CS4 (no errorcorrection, highest data rate). The Vodafone GPRS network, and most handsets, will only support CS1 and CS2.The high incidence of errors when CS3 and CS4 are used prohibits their use under most circumstances.

The second way of increasing bandwidth is to utilise multiple timeslots. Handsets will be described by the maximumnumber of timeslots that they can use on the downlink, plus the number of timeslots that they can use on the uplink,for instance ‘2+1’, ‘4+1’, ‘3+2’. It is expected that the majority of data will be received by the handset rather thantransmitted by it.

Timeslots will be dynamically allocated according to availability. Up to 8 timeslots are available on any given channelwithin a cell and the management of resources will be negotiated between the handset and the network. GSM willgenerally take priority over GPRS and so from time to time availability may be reduced as the number of voice callersrises. However, the advantage of GPRS is that as soon as a timeslot becomes available it can benefit many datausers.

Table 4 lists the theoretical maximum transmission rates (throughput) using the different coding schemes andutilising one or more timeslots. Up to four timeslots may be available for GPRS on a given live cell, but this may bedynamically adjusted against the requirements of GSM users on the same cell when the service becomes live.Under coding scheme 2 (CS2) for example, each timeslot provides 13.4Kbps (K bits per second). This provides apayload of approximately 12Kbps.

Table 4 - Throughput Capabilities of GPRS

Coding Scheme 1(CS1)




1 Timeslot 9.05 Kbps 13.4 Kbps 15.6 Kbps 21.4 Kbps

2 Timeslots 18.1 Kbps 26.8 Kbps 31.2 Kbps 42.8 Kbps

3 Timeslots 27.15Kbps 40.2 Kbps 46.8 Kbps 64.2 Kbps

4 Timeslots 36.2 Kbps 53.6 Kbps 62.4 Kbps 85.6 Kbps

A detailed example describing how to calculate the realistic throughput can be found in Section 8.

1.7 What About WAP?

Wireless Application Protocol, WAP, allows mobile equipment to browse the Internet. It is a bearer independentservice and therefore will run over GPRS as well as GSM.

GPRS handsets supporting WAP V1.1 will be available from about October 2000 and handsets supporting WAP V1.2will be available at the launch of the service.

In the interim, WAP emulation software can be run on the PC to convert data and present it, as would a dedicatedWAP phone. Such an application may be included in the development environment provided.



The development suite consists of an office area with seating space for two developers and a Vodafone supportengineer. A workstation PCs is supplied, networked into the GGSN of the GPRS network. This can be booted intoeither Windows NT 4, or Windows 2000 and is intended for use on the server-side of applications testing. Astandalone laptop bootable into Windows 98 or Windows 2000, and with various GPRS utilities, is available for usewith the GPRS handsets. A range of GPRS handsets is available to developers. The models currently available are:

• Ericsson R520

• Motorola T260

• Mitsubishi Trium

Alternatively, GPRS SIMs suitable for use on the test network can be supplied to developers who prefer to use theirown handsets.

We will try to accommodate requests for additional equipment or different operating systems but it will not always bepossible or practical for us to do so. In general, the final responsibility for machine configuration lies with thedeveloper.

The most accessible method of demonstrating and using GPRS is via the Dial-up Networking facilities of MicrosoftWindows, or similar facilities provided by other operating systems. For the purposes of these examples, Dial-upNetworking will be referenced. In practice, any TCP/IP protocol stack should be able to be used.

The software on the laptop includes;

• Reflection – A terminal application

• Assorted TCP/IP demonstration utilities suitable for GPRS

• The Vodafone Wireless Login Client software

The network configuration of the development suite is illustrated below. The PC is connected to the GPRS testnetwork node. By putting the phone in the same office, an end-to-end testing environment is obtained, wheredevelopers can control both client and server sides of their application.

10.37.4.147Win2K ServerVFMKNY238192.168.0.1

VosnetDNS 10.37.3.1&2

Gateway 10.37.4.254

GPRS

Dower BTS

10.37.4.91

Developer's Machine10.37.4.x

Mask: 255.255.255.0Gateway: 10.37.4.254

Hub

Web server192.168.0.2

192.168.1.xx=SIM number

Figure 1 - The Vodafone GPRS Development Environment

2. GETTING STARTED



2.1 Caveats

In the early stage of the GPRS programme, the network control nodes are running prototype software versions. Thetest network may therefore suffer occasional outages, sometimes without notice.

Similarly, the GPRS handsets in use are generally still prototypes. Their software is frequently being upgraded andconsequently the information given in this document may not be up-to-date. The phones themselves will not be asstable, well behaved or well documented as would be expected of production handsets.

Vodafone-owned development machines will generally be restored to a clean state between uses by differentbusiness partners, however Vodafone cannot be held responsible for the security of software or data left on itscomputers after testing. The onus is on developers to remove sensitive information from Vodafone equipment.

2.2 Preliminary setup

The TA and laptop normally use a serial interface to communicate. Both the Motorola and Ericsson phonessupport cable and IR serial connections. Actual connectivity details will depend on the type of connection, theoperating system on the laptop and the software being used.

1. Power on the laptop and allow to boot

2. Power on the phone

3. Check that the phone has attached1 to the test network. Depending on the phone, this will generally justinvolve looking for the text PTT Telecom appearing in the display.

4. For phones with direct cable connection, make all necessary connections. For infrared connectivity, lineup the IrDA ports on the phone and the laptop so that a link can be established. The valid I/R link will beconfirmed in the System Tray.

2.3 Connecting with Reflection and Dial-up networking

This section describes how to use standard Windows facilities to perform the context definition, attach and context-activation steps. These instructions should be easily adaptable to different platforms (e.g. PDAs) and operatingsystems. Some form of communications package is required to issue the commands to the handset, and we haveused Reflection as it supports scripted commands (including waiting for responses). The commands could also beissued directly from HyperTerminal, which comes as a standard component in all desktop Windows versions.

2.3.1 GPRS Attach and Context Activation

Before Dial-up Networking can be used, AT commands must be issued to the phone to attach to the GPRSservice and activate a valid context. Some handsets automatically attach The AT commands required for thisare stored in a macro.

1. Open the Reflection session for the GPRS device being used. A shortcut to a session that has alreadybeen configured for the specific device will be present on the desktop.

2. Type AT and verify that OK is received. If so, proceed. Otherwise, check the setup and configuration,then resume.

3. There are three customised buttons in the toolbar, labelled ‘Attach’, ‘Set IP Address’ and ‘Detach’.

4. Click ‘Attach’2 and wait for the ‘OK’ response. You should see:AT+CGATT=1OK

5. Click ‘Set IP Address’ and wait for the three AT commands to be issued and receive a positiveresponse. Depending upon the GPRS phone provided, you may see:

1Depending on the handset, this may be a GPRS Attach, or it may just be an IMSI (traditional GSM) Attach to the testnetwork.2 If the phone has automatically GPRS-attached on power-up, this is of course redundant. It doesn’t do any harm inany case though.



Ericsson Session:AT+CGDCONT=1,”IP”,”WWW.ERICSSON.SE”,”192.168.1.9”,1,1OKAT+CGQREQ=1,2,1,3,9,18OKAT+CGQMIN=1,2,1,3,9,18OK

Motorola Session:AT+CGDCONT=1,”IP”,”WWW.ERICSSON.SE”,”192.168.1.9”,1,1OKAT+CGQREQ=1,2,1,3,9,18OKAT+CGQMIN=1,2,1,3,9,18OK

Mitsubishi Session:AT+CGDCONT=1,”IP”,” WWW.ERICSSON.SE”,”C0A80109”OKAT+CGQREQ=1,2,1,3,9,18OKAT+CGQMIN=1,2,1,3,9,18OK

Note that there are some differences between the syntaxes of the commands listed above. Someparameters are optional within the string, which is why there are a varying number of parameters inthe AT+CGDCONT command.

However all the context definition commands have specified a static PDP address to be used as theIP address of the GPRS connection. The Ericsson and Motorola devices require this to be specifiedin decimal format, e.g. “192.168.1.9”, but the Mitsubishi requires the IP address to bespecified as a hexadecimal value, e.g. “C0A80109”. The parameter itself is a string value,although the quotation marks may be omitted. On the test network, static addresses are simply192.168.1.x where x is the number o

If ERROR is returned to any of the commands, issue AT so as to solicit an OK response. This willallow the macro to complete, after which you should try and determine why the command could notexecute successfully (Is the phone properly connected and switched on?).

6. ‘Disconnect’ the reflection session (Icon should become ) and minimise the window. At this point,the TA is attached to the GPRS network. It does not yet have an active context; the context has merelybeen defined. Disconnecting the Reflection session allows Dial-Up Networking to be able to use thedevice by freeing up the COM port. Minimising the Reflection session will also remind you to perform afull detach when finished.

2.3.2 Dial-Up Networking

A GPRS device that is attached on the network and has a context defined locally may activate that contexton the network and commence data transfer or remain idle.

It is possible to activate a context manually by issuing the appropriate AT commands, but context activationwill be carried out implicitly when the GPRS service is dialled.

The AT Dial command is supported within the GPRS subset of commands for backwards compatibility. TheService Code that is dialled is always 99, but other parameters may be specified hence the actual dial stringused for the Ericsson and Trium is *99***1#, while for the Motorola it is *99#. The format of this stringis explained further on. The Dial-Up Networking sessions have already been configured with this number.



A shortcut to the default Dial-Up Networking sessions for both the Ericsson and Mitsubishi devices arelocated on the desktop. Double click these and click ‘OK’ in the dialog box. No password is required.

When the session is established, an icon will be placed in the system Tray indicating the connection status.For more detailed statistics, the tool Dial-Up Networking Monitor may be used.

2.3.3 Ending The Session

It is important to detach properly from the GPRS network.

1. Disconnect the Dial-Up networking connection

2. Restore the Reflection window

3. Reconnect to the device by clicking the connect/disconnect button in the toolbar (Icon should become)

4. Click ‘Detach’ from the toolbar

The Reflection window may be closed if desired.

2.4 Connecting with Vodafone’s Wireless Login Client

The Wireless Login Client automates the setting up of a GPRS connection, including setting the IP address, definingthe context, performing an Attach and setting up the context. Documentation and help for this software, and theprogram itself, can be obtained when using the development facility.

2.5 Testing the IP Link

To test the GPRS link, open a DOS window and enter

ping 192.168.186.97 –w 5000

This will ping the ISP server attached to the GPRS Gi interface. The –w 5000 is to ensure enough time isleft for a response to be received.

You should then be able to obtain an IP connection through to the server side of the application under test. Ifaccess to Web content is required this can usually be arranged via a proxy server.



GPRS is able to support all protocols that sit above IP. IP itself can be run over a wide range of lower level protocols,including radio bearer services such as GPRS.

The Point-to-Point Protocol, PPP, as operated widely across the Internet, is one of the simplest methods of workingwith IP over GPRS since the majority of modern operating systems support it.

Figure 2 - Protocol Stack for IP Based Services

The GPRS device is a Terminal Adaptor (the terminology ‘modem’ is technically incorrect for all GSM/GPRSdevices). It therefore provides an interface at the R reference point in the ISDN model of network access points.

Each interface at the R reference point can only support one PPP connection and each PPP connection can onlyhost one IP session. The consequence is that only one PDP context can be activated per interface at the Rreference point, whilst in PPP mode.

Section 9 describes the protocols used in the transmission plane in more detail.

3.1 Establishment Sequence

PPP is a Link Layer protocol. When IP over PPP is requested, the Link Control Protocol is set up between the TEand the ME. After this, the Network Control Protocol is negotiated and this includes communications across the radiolink to attach the GPRS device and to activate the GPRS context.

The detailed sequence of messages that are exchanged between various elements in the system is not describedhere.

3. IP OVER PPP

IP Relay

Application

PPP

IP

PPP

Layer 1 Layer 1

GPRS Bearer

TE TA

R RefPoint



Most GSM Terminal Adaptors support a comprehensive range of AT commands based upon the GSM 07.07technical specification. ETSI have based the command syntax around the V.250 (formerly V.25ter) guidelines andthe command interface to a GSM TA is intended to meet the V.250 specifications.

Those AT commands specific to GSM are prefixed by ‘+C’, where the ‘+’ identifies it as an extended command andthe ‘C’ is a reference to the Cellular nature of the GSM system.

The AT commands defined for GPRS begin with ‘+CG’, where the ‘G’ stands for GPRS. GPRS is still a cellularbased radio service.

Class-C GPRS devices, especially those that are only Class-CG, have limited, if at all, support for non-GPRS ATcommands. The Mitsubishi Trium has more extensive support for GSM and GPRS AT commands that the EricssonR320 and so responses to the examples listed below may differ from device to device.

A response of ERROR to any AT command probably means that the command has yet to be implemented in thatdevice. Note that the prototype Ericsson handsets may respond with ERROR to an attach, even if the attach wassuccessful.

4.1 Informative Examples

4.1.1 Querying the GPRS Device

This set of examples show some AT commands that can be issued without needing to attach to the serviceor activate a context. The responses presented by different devices may vary.

These are in addition to non-GPRS specific AT commands that are otherwise described in GSM 07.07.

Command AT+CGATT=? Query available attach statesResponse +CGATT: 0, 1 Can be detached or attachedCommand AT+CGATT? Request current attachment stateResponse +CGATT: 0 Currently detachedCommand AT+CGCLASS=? Query available classesResponse +CGCLASS: A, B, C, CG, CC List of available classes in descending order of

functionality, as supported.Command AT+CGREG=2;+CGREG? Request registration informationResponse +CGREG: 2,1,”11AE”,”0003” Presents the <lac> and <ci> informationCommand AT+CGSMS=? Query SMS optionsResponse +CGSMS: 0,1,2,3 List of supported services

4.1.2 Mobile Initiated Context Activation

In this example, the TA begins in the normal V.250 Command State, i.e. AT commands can be entered. Thecommand +CMEE has been issued so that any errors are reported with a diagnostic result code.

The GPRS AT commands are then issued in a verbose sequence to illustrate the processes involved inactivating a GPRS context.

Command AT+CMEE=1 Extended error reportingResponse OKCommand AT+CGDCONT=1,”IP” Define a context locally as cid=1, using IP as the

PDPResponse OKCommand AT+CGATT=1 Explicitly attach to the GPRSResponse OKCommand AT+CGACT=1,1 Activate the context with cid=1Response OK

4. AT COMMANDS FOR GPRS



Three discrete steps can be identified above:

• Define the PDP context

• Attach to the GPRS network

• Activate the PDP context.

It is not generally necessary explicitly to activate a GPRS context because the act of dialling the GPRSService Code will automatically active the specified context if it is not already active.

In the above example, no <PDP_Address> was specified within the +CGDCONT command. The service willtherefore assign an address within its range, provided this facility is available. The IP can be queried oncethe context is active;

Command AT+CGDCONT? Request context informationResponse +CGDCONT: 1,”IP”,,,0,0

OKThis method does not return the PDP_Addressunless it was explicitly provided in the+CGDCONT command

Command AT+CGPADDR=1 Request PDP_Address for cid=1Response +CGPADDR: 1, “192.168.1.14”

OKAssigned address is returned

4.1.3 Entering the Data State

There are two ways to enter the Data State in GPRS (analogous to making a call in circuit switchednetworks). A new command, +CGDATA, is provided which causes the MT to perform whatever actions arerequired to establish communication between the TE and the network. This includes activating one or morePDP contexts if none are already activated.

In addition, the Dial command (i.e. ATD) is maintained in the GPRS environment, as an alternative method to+CGDATA, to provide backwards compatibility with existing applications. This method will also activate oneor more PDP contexts if none are already active.

Command AT+CGDATA=”PPP”,1 Connect using PPP as the L2P and using contextwith cid=1

Response CONNECTAd-Hoc IP packets exchanged

L2P call termination method Call clear request as per L2PResult NO CARRIERCommand AT+CEER Query call termination reasonResponse +CEER: <xxx> Where <xxx> is a manufacturer specific report.

Refer to TA documentation.

A special GPRS Service Code is defined with a value of ’99’, which identifies a request to use GPRS.Further parameters on the ATD command line are delimited by the asterisk character (*) and the commandstring is terminated with a hash (#). This syntax is specified in GSM 02.30.

The basic content for this parameter is ATD*99***1#, which will activate the specified context (1)pending further instruction.

Command ATD*99***1# Connect to GPRS serviceResponse CONNECTAd-Hoc IP packets exchanged

L2P call termination method Call clear request as per L2PResult NO CARRIERCommand AT+CEER Query call termination reasonResponse +CEER: <xxx> Manufacturer specific result code



4.1.4 Abnormal Call Clear

GPRS Attaches and active contexts can recover from the MS going briefly out of coverage, or from beingsubject to intermittent interference. However any communication in progress will of course be interrupted. Itis up to the application to deal with, and recover from such interruptions in a sensible manner.

If the connection is lost at any time, the ME shuts down the PPP and it returns to the V.250 Command State.This is accompanied by the final result code NO CARRIER.



A laptop PC can be provided with the following configuration settings for some (but not all) combinations of handset,connection and operating system.

q Modem definitions

q Dial-up Networking connections

q Reflection sessions

q Macro scripts

q Login Client configurations

Example settings for two handsets on Windows 98 are given below. Only those settings that have a value or mustabsolutely not have a value are listed. I.e. if a dialog box presents a checkbox and the box is not checked, theparameter will not be listed.

5.1 Modem and Dial-Up Networking Settings

The following settings are appropriate for Ericsson GPRS devices that use the Infrared port and Motorola T260handset, connected directly to COM1 via a cable. As different combinations are tested, configuration files will bemade available.

Table 5 - Modem and Dial-Up Networking Configuration Settings

Modem Settings

Title “Ericsson R520” “Standard 33600 bps Modem”

General

Port Virtual Infrared COM port Communications Port (COM1)

Maximum Speed 115200 57600

Connection

Data Bits 8 8

Parity None None

Stop Bits 1 1

Cancel the call if not connectedwithin

60 seconds Not specified

Options

Wait for credit card tone 8 seconds 8 seconds

Display modem status SET SET

Advance Port Settings

Default settings Default settings

Advanced Connection Settings

Flow Control SET

Hardware (RTS/CTS)

SET

Software (Xon/Xoff)

Extra settings None None

Append to log Optional but off by default Optional but off by default

Dial-Up Networking Properties

Title “Ericsson DUN” “Motorola”

General

5. APPENDIX 1 – CONFIGURATION SETTINGS



Area codes are not used in GPRS. With the box “Use area code and DiallingProperties” unchecked, the Area code field is greyed out.

Telephone number *99***1# *99#

Connect Using Ericsson GPRS Prototype Standard 33600 bps Modem

Server Types

Type of Dial-Up Server PPP: Internet Windows NT Server,Windows 98

PPP: Internet Windows NT Server,Windows 98

Record a log file for thisconnection

SET SET

TCP/IP SET SET

TCP/IP Settings

IP Address Server assigned IP Address Server assigned IP Address

Server Addresses Server assigned name serveraddresses

Server assigned name serveraddresses

Use default gateway on remotenetwork

SET SET

Scripting and Multilink These two pages have no customised settings, but for reference, no script filesare defined or used. If you wish to define logon scripts for your own services,please do so in a copy of the Dial-Up Networking settings.

Start terminal screen minimized SET SET

5.2 Reflection Session Configurations

For each device, a terminal session has been defined within the Reflection terminal application. These are used toissue necessary AT commands to the GPRS device prior to using Dial-Up Networking. The key difference betweeneach session is that the correct device is chosen and operated at the correct speed. The macro for defining acontext is identical for both cases.

Please do not change the settings for these sessions. If you wish to experiment with different settings, please do soon a copy of the session.

5.2.1 Custom Toolbar

To avoid having to remember the AT command strings, and to prevent the mistyping of them, three buttonshave been added to the toolbar. One of these calls upon a macro, a sample of which is listed below.

The settings for the three customised buttons are as follows

Table 6 - Custom Toolbar Objects in Reflection

Label Attach Set IP Address Detach

Tooltip text Attach Define Context Detach

Action Send text Macro Send text

Text to send AT+CGATT=1<CR> AT+CGATT=0<CR>

Macro type Visual Basic

Macro Name GPRSCon



5.2.2 Macro Contents

This information is provided for reference (parameters may vary). The following macro performs threefunctions,

• Defines a suitable context to be activated later

• Requests a particular QoS level

• Specifies a minimum acceptable QoS level.

The QoS values are not fully implemented but the sequence provides an idea of a typical GPRS sequence.

The macro issues each of the AT commands and only continues if OK is received. Therefore, if there shouldbe a problem and ERROR is returned, simply type ‘AT’ to solicit an OK response. The script should then runto completion, but it will be necessary to find out why the error occurred.

Attribute VB_Name = "NewMacros"Sub GPRSCon() '' GPRSCon macroAttribute GPRSCon.VB_Description = "Macro created 26/01/00 by gprsuser4"' Macro created 26/01/00 by gprsuser4' On Error GoTo ErrorHandler

Dim username As String

Const NEVER_TIME_OUT = 0

Dim LF As String ' Chr$(rcLF) = Chr$(10) = Control-J Dim CR As String ' Chr$(rcCR) = Chr$(13) = Control-M

LF = Chr$(rcLF) CR = Chr$(rcCR)

username = Chr$(22) & CR With Session If .Connected = False Then .Connect End If

' .WaitForString Chr$(22) & CR, NEVER_TIME_OUT, rcAllowKeystrokes ' Press EditPaste (Insert the Clipboard contents at the cursor position). ' Reflection has recorded the record-time contents of the clipboard. ' If you want to use the playback-time contents of the clipboard, ' Uncomment the following line and delete the appropriate record-time

data. ' Paste .Transmit "at+cgdcont=1,""IP"",""WWW.ERICSSON.SE"",""C0A80109""" & CR .WaitForString LF & "OK" & CR & LF, NEVER_TIME_OUT, rcAllowKeystrokes .Transmit "at+cgqreq=1,2,1,3,9,18" & CR .WaitForString LF & "OK" & CR & LF, NEVER_TIME_OUT, rcAllowKeystrokes .Transmit "at+cgqmin=1,2,1,3,9,18" & CR .WaitForString LF & "OK" & CR & LF, NEVER_TIME_OUT, rcAllowKeystrokes ' Exit Sub

ErrorHandler: .MsgBox Err.Description, vbExclamation + vbOKOnly

End With ' Recording stopped at 16:11:00.84.

End Sub



A script has been written for the Reflection terminal application to automate the attach and definition of context andQuality of Service parameters for a GPRS handset. It may also be used to detach from the service when all activityis complete.

6.1 How To Use

A shortcut titled GPRS Connection Script has been placed on the desktop to allow a GPRS handset to be attachedor detached from the service. (If it is already attached, a detach will be performed and vice-versa).

Double-click on the icon to run it. The session will run in a minimised state and will remain hidden from view until ithas finished. A dialog box will indicate success or failure of the script.

If attaching a device, once the script has finished, Dial-Up Networking can be used to establish a connection acrossthe GPRS.

Once the Dial-Up Networking session has been disconnected, this script should be run again to detach the devicefrom the service.

The script is flexible and can be configured to work with a wide range of handsets. This means that as new handsetsbecome available, the script should still be able to be used (configuration settings will need updating).

6.2 Location of the Files

A shortcut should reside on the desktop to facilitate access to the service.

The standard location for Reflection scripts is the ‘User’ folder as shown in the settings, below.

The default location of the configuration file is the root of the C: drive. This can be altered from within the script.

If the script file is not found, it will be created based upon settings requested of the user.

6.3 Shortcut on the Desktop

The script is activated from a shortcut on the desktop. The shortcut must be setup with the following parameters,where paths should be amended as required.

Target: "C:\Program Files\Reflection\r2win.exe" /N /RBS "C:\ProgramFiles\Reflection\User\Gprs\Attach.rbs"

Where:

"C:\Program Files\Reflection\r2win.exe" Points directly to the executable Reflection application

/N Prevents Reflection splash page from being shown

/RBS "C:\Program Files\Reflection\User\Gprs\Attach.rbs" Path to the script

Additional settings:

Run: Minimized or Normal Hide or show the session, as desired.

6.4 Progress Indications and Script Behaviour

The script can either run completely silently or with the Reflection session window open so that the AT commandsand their responses can be observed. This may help with understanding the nature of any problems that may occur.A parameter in the configuration file, Show Progress, can be either True or False to enable or disable this feature.

When the actions of the script have finished, the COM port is released so that other programs, such as Dial-UpNetworking, can be used.

The script may also be configured to close Reflection completely when done. The configuration parameter ExitWhen Done controls this. If the parameter is set to False, Reflection remains open (but disconnected). Theconnection may be re-established so that AT commands can be entered to the device if desired.

6. APPENDIX 2 - CONFIGURATION FOR VODAFONE GPRS CONNECTION SCRIPT



6.5 The Configuration File

Path: C:\GPRSCon.cfg

Vodafone may redistribute this file from time to time as new handsets become available and if new Modem types aredefined to use them.

# Vodafone GPRS Connection Script Parameters# This configuration file is used by the Reflection script 'Attach.rbs' and contains# parameters that may be changed if necessary.# Deleting Essential lines of configuration will cause the script to request new values.# Essential configuration parameter values can be empty to ignore that parameter altogetherContext=1APN=WWW.ERICSSON.SE

# The IP Address should be in decimal format. Will be converted to hex if necessary.IP Address=192.168.1.1

# The Context ID in the parameters below does not have to match the Context value above.AT+CGQREQ=1,0,0,0,0,0AT+CGQMIN=1,0,0,0,0,0# End of Essential configuration parameters.Def QOS=1,2,1,3,9,18

# This parameter keeps the Reflection window open so that progress can be reviewed.Show Progress=True

# By default, the Reflection session will terminate when complete.Exit When Done=False

# List of known handsets: 'Result of ATI0-9 command','Format specifier for IP addresses'# If ATI is not supported or handset not listed, 'dec' is assumed.# Attach Options (one of): AD=Alternate Attach/Detach; AA=Always Attach# QOS Options (one of): ConfigQOS, DefaultQOS, AskForQOS# Must also specify which AT parameters require Quotes; PDP Type, APN, PDP AddressHANDSET=GSM DATA CARD MITSUBISHI ELECTRIC V.4.021 BETA,hex,AD,ConfigIP,AskForQOS,QUOTES,QUOTES,QUOTESHANDSET=Ericsson GPRS Prototype Modem,dec,AA,ConfigIP,AskForQOS,NOQUOTES,QUOTES,QUOTESHANDSET=R520m Infrared Modem,dec,AD,ConfigIP,AskForQOS,NOQUOTES,QUOTES,QUOTES

# List of modems defined in Control Panel that GPRS devices will use.# COM ports can also be listed as available.MODEM=Generic Infra Red Device,COM4

Lines highlighted in Bold are considered ‘essential’ configuration elements. If these lines are not found, suitablevalues for them will be requested of the user.

It is valid for a line to have no value, e.g. “IP Address=”. This will mean that no value will be specified in commandsthat might take that argument as a parameter. The IP address in this sample is an example only. Only the addressallocated should be used.

If there are no Modem types, a connection at 38400 baud, 8 bits and no parity will be set up on COM1. All COM portconnections are set up at 38400 baud with a parity of 8/None.

6.5.1 Resetting The Config File

If the script does not appear to be specifying the correct settings, e.g. the APN is wrong or missing, the configfile has probably been amended incorrectly.

The best way to sort things out is to reset only that part of the configuration that has a problem.

• Open the file in a text editor, such as Notepad

• Delete only the line in question, e.g. the whole line that says “APN=…”

• Save the config file and quit the editor

• Restart the script

The parameter should be requested if it is an essential parameter.



6.5.2 Manual Modifications

Manual modifications to the config file are allowed. For instance, the parameters “Always Attach” and “UseDefault QOS” are manual override settings. These parameters take True or False as their argument.

Also, new handsets and their required modem types must be added manually, as per the template andexamples.

6.6 Flowchart

The sequence of actions for the script is described by the flowchart, below. It is possible to hide the action of thescript by changing the “Show Progress” parameter to False.

Figure 3 - Flowchart for GPRS Connection Script

If the config file is missing all of the “essential” parameters, these will be requested. The file will then be saved.

It is necessary to choose a connection mode so that the device can be tested. The modem and connection types arespecified in the config file, although COM1 is always available.

Once connected, the script will check to see if the device is present by issuing AT. It will timeout after a few secondsif nothing is detected and report an error.

The ATI command is executed next to detect the identity of the device attached. ATI0 to ATI9 are issued insequence until a match is found to a defined handset. If no match is found, a series of default parameters areassumed.

Some of the earliest GPRS handsets had limited support for GPRS AT commands. A parameter, “Always Attach”,can be specified for certain devices, such as the Ericsson R320 Prototype, to override the normal action of this script.If the parameter is False, the script will attempt to perform an attach if the device is currently detached and vice-versa.

Start

Read config file

Input any required'essential' parameters

and save file

Select Modem/Connection

Send AT to device

OK?

Identify the specificdevice (issue ATI)

Yes

Finish

Report error/success

No

HandsetParameters:

AlwaysAttach?

Already attached?

Detach

Attach

Define PDP Context

Specify QOSParameters

No

Yes

Yes

No

Input any additionalconfig parameters



Most of the configurable handset parameters are applied during the definition of the PDP context. The APN and IPaddress are taken from the configuration parameters and some parameters may need to be enclosed in doublequotes. Furthermore, some devices require the IP address to be in decimal format and others require this to be inhexadecimal. The script will take care of all of these requirements on a per handset basis, if configured to do so.

When the script has finished executing, the session will terminate completely if “Exit When Done” is True. If thisconfiguration parameter is False, the Reflection session will remain open but in a disconnected state. In this way,Dial-Up Networking can be used, or the session can be reconnected to allow AT commands to be typed manually.

6.7 Handset Definitions

The syntax requirements of each handset may vary and the configuration file can reflect these requirements. Ahandset definition may look as follows:

HANDSET=<ATIn Result>,<IP Mode>,<Attach Options>,<IP Options>,<QOSOptions>,<Quotes?>

e.g.HANDSET=R520m Infrared Modem,dec,AD,ConfigIP,AskForQOS,QUOTES,QUOTES,QUOTES

Where;

<ATIn Result>: A suitable descriptive result from any of ATI0 to ATI9

<IP Mode>: “hex” or “dec” for format of IP address in +CGDCONT. Must be the parameter immediatelyafter <ATIn Result>

<Attach Options>: AD=Alternate Attach/Detach; AA=Always Attach

<IP Options>: ConfigIP=Use the IP address in the Essential parameters section; AskForIP=Override the IPaddress in the Essential Parameters with a value requested of the user.

<QOS Options>: ConfigQOS=Use the QOS string in the Essential parameters section; DefaultQOS=Use thedefault QOS string for both +CGQREQ and +CGQMIN commands; AskForQOS=Override thestored QOS values with a string requested of the user.

<Quotes>: A list of three flags to identify if double quotes (“) must be placed around certain parameters inthe +CGDCONT command. The parameters that may require quotes around them are: PDPType (e.g. IP); APN Address (e.g. WWW.ERICSSON.SE); PDP Address (e.g. 192.168.1.x).The handset definition requires a value of QUOTES or NOQUOTES.

6.7.1 Adding A New Handset

As new handsets become available, the configuration options described above can be specified to allow thathandset to operate correctly with this script. A small amount of preparation is required first to determine thecorrect settings. This preparation involves typing the AT commands manually to find out the syntaxes of thevarious commands.

The steps are as follows

1. Open the file C:\GPRSCon.cfg in Notepad so that details can be recorded as they are determined. Inthe section where the handsets are located, add a new line and enter the text HANDSET=

2. If the handset is supplied with a modem configuration file, install this.

3. Open a Reflection session and attempt to communicate with the device. Select a defined Modem typeor choose the COM port to which the handset is connected. For COM ports, the speed (try 38400) andparity (use 8/None) should also be selected.

4. Type AT and look for the OK response. If nothing is seen, return to step 3. and choose different settingsuntil OK is seen to the AT command.

5. Get the Modem Information string. Type ATI0 (ATI Zero) and hit return. If what is returned seems tosuitably describe the handset, copy the string into the clipboard, then paste it after the Equals sign onthe new HANDSET line in GPRSCon.cfg. If ATI0 did not provide a suitable response, try ATI1 (ATIOne) then ATI2 up to ATI9 until an acceptable response is found.



6. Next it is necessary to identify whether the handset requires IP addresses to be in decimal orhexadecimal format. This parameter must be the next parameter after the Modem Information string.Unless you know otherwise, just enter ,dec for now (where the comma is used to separate this field fromthe one before)

7. Type the AT command AT+CGATT? And note the response. If the response is +CGATT: 0 or+CGATT: 1 then the next parameter on the HANDSET= line should be AD. If either of theseresponses is not observed, type AA.

Response to AT+CGATT? Attach Option

+CGATT: 0 AD

+CGATT: 1 AD

Anything else AA

The next two parameters, <IP Options> and <QOSOptions> are up to the user. If the values for these parameters within theconfiguration file are always going to be correct, these can be set to ConfigIP and ConfigQOS respectively. If theywill constantly vary, set them to AskForIP and AskForQOS. The Quality of Service options have an additionalparameter that allows a default value to be used, DefaultQOS.

8. The final set of parameters can only be obtained through trial and error. Try the following permutationsof parameters until the handset responds with OK. Then add the parameters to the HANDSET= line asshown. For example, AT+CGDCONT=1,”IP”,”WWW.ERICSSON.SE”,”1.2.3.4”

Arguments to AT+CGDCONT= Add this to line in GPRSCon.cfg

1 1,”IP”,”WWW.ERICSSON.SE”,”1.2.3.4” QUOTES,QUOTES,QUOTES

2 1,IP,WWW.ERICSSON.SE,1.2.3.4 NOQUOTES,NOQUOTES,NOQUOTES

3 1,IP,”WWW.ERICSSON.SE”,”1.2.3.4” NOQUOTES,QUOTES,QUOTES

4 1,”IP”,WWW.ERICSSON.SE,”1.2.3.4” QUOTES,NOQUOTES,QUOTES

5 1,IP,WWW.ERICSSON.SE,”1.2.3.4” NOQUOTES,NOQUOTES,QUOTES

6 1,”IP”,”WWW.ERICSSON.SE”,1.2.3.4 QUOTES,QUOTES,NOQUOTES

7 1,IP,”WWW.ERICSSON.SE”,1.2.3.4 NOQUOTES,QUOTES,NOQUOTES

8 1,”IP”,WWW.ERICSSON.SE,1.2.3.4 QUOTES,NOQUOTES,NOQUOTES

9. If all of these permutations respond with an ERROR it may be because the IP address must be inhexadecimal format. Repeat the series of arguments as follows until OK is received.

Arguments to AT+CGDCONT= Add this to line in GPRSCon.cfg

9 1,”IP”,”WWW.ERICSSON.SE”,”01020304” QUOTES,QUOTES,QUOTES

10 1,IP,WWW.ERICSSON.SE,01020304 NOQUOTES,NOQUOTES,NOQUOTES

11 1,IP,”WWW.ERICSSON.SE”,”01020304” NOQUOTES,QUOTES,QUOTES

12 1,”IP”,WWW.ERICSSON.SE,”01020304” QUOTES,NOQUOTES,QUOTES

13 1,IP,WWW.ERICSSON.SE,”01020304” NOQUOTES,NOQUOTES,QUOTES

14 1,”IP”,”WWW.ERICSSON.SE”,01020304 QUOTES,QUOTES,NOQUOTES

15 1,IP,”WWW.ERICSSON.SE”,01020304 NOQUOTES,QUOTES,NOQUOTES

16 1,”IP”,WWW.ERICSSON.SE,01020304 QUOTES,NOQUOTES,NOQUOTES

10. If a hexadecimal IP address was necessary, modify the dec parameter after the Modem Informationstring to hex.



This section provides a summary of the AT commands that have been defined for GPRS. They are fully described inGSM 07.07. Support for these commands within devices is likely to be extended as the functionality is achieved.

There are two types of action command: those that are associated with parameters that may be able to be set, readand tested, and those that are not.

To set the value, the command is followed by an equals (=) sign and a list of parameters compatible with the syntaxof the command, e.g. AT+CGATT=1

The current value is read by appending a question mark (?) to the command, e.g. AT+CGATT?

The range of acceptable values can be tested by appending the command with ‘=?’, e.g. AT+CGATT=?

7.1 GPRS AT Commands

Table 7 - Summary of AT Commands for GPRS

Command Description+CGACT PDP context activate or deactivate+CGANS Manual response to a network request for PDP context activation+CGATT GPRS attach or detach+CGAUTO Automatic response to a network request for PDP context activation+CGCLASS GPRS mobile station class+CGCLPAD Configure local triple-X PAD parameters+CGDATA Enter data state+CGDCONT Define PDP context+CGEREP Control unsolicited GPRS event reporting+CGPADDR Show PDP address+CGREG GPRS network registration status+CGQMIN Quality of service profile (minimum acceptable)+CGQREQ Quality of service profile (requested)+CGSMS Select service for MO SMS messages

Table 8 - Summary of Existing GSM AT Commands with GPRS Extensions

Command Description+CEER Extended error report (refer to 07.07)+CMEE Report mobile equipment error (refer to 07.07)+CR Service reporting control (refer to 07.07)+CRC Cellular result codes (refer to 07.07)

Table 9 - Summary of AT Commands for GPRS Modem Compatibility Mode

Command DescriptionA Answer - manual acceptance of a network request for PDP context

activationD Dial - request GPRS serviceH On-hook - manual rejection of a network request for PDP context activationS0 Automatic answering control - automatic acceptance of a network request

for PDP context activation

7. APPENDIX 3 – GPRS SPECIFIC AT COMMANDS



Section 1.6 introduced the way bandwidth is allocated and utilised in GPRS. The table in that section listed themaximum data rate per Coding Scheme when one to four channels are used. The user data rate (payload data) isalways going to be less than this because of the overhead introduced by all of the necessary protocols. Since packetsizes vary, and given that GPRS is specified to be used with a number of different Layer 2 Protocols it is not possibleto list a single user data rate to meet all requirements.

This section provides some examples of data rate calculations with respect to typical uses. GPRS uses much of thesame infrastructure as GSM and so is bound by some of the design decisions behind that technology, so a briefintroduction to some relevant aspects of GSM is provided.

8.1 GSM and the Air Interface

The basic data rate for most digital networks is 64Kbps (K bits per second – NB. bits, not bytes). This figure isarrived at through sampling theory in the following manner.

The human ear can detect sounds in the range of a few hundred Hz up to around 20KHz, but most of the frequenciesrequired to recognise human speech are in the range between 300Hz and 4000Hz. This requires the voice to besampled 8000 times per second. Each sample is quantised to one of 256 values, requiring 8 bits of data per sample.Hence, 8000 samples per second x 8 bits per sample = 64Kbps.

This data rate is fine for PSTNs, where bandwidth is not too much of an issue and error rates are also not soconsequential. However, the air interface is a far more limited resource and is much more difficult to work with. GSMemploys coding schemes optimised for voice that provide compression and forward error correction. This codingscheme takes samples of speech 20ms in length and turns them into a Radio-Block of 456 bits. The Radio-Block issent in four bursts across successive timeslot periods, along with additional bits of information required by the airinterface.

Each cell in the GSM frequency spectrum provides enough capacity for one control timeslot and seven full-rate voicetimeslots, i.e. the air bandwidth is time-division multiplexed eight ways.

The result is reasonable, albeit not perfect, speech reproduction that is acceptable for a wide variety of applications.

8.2 GPRS Data

GPRS is an extension to GSM and uses the same frequencies, air interface protocols and in many cases, the samecells as GSM. Therefore, the Coding Schemes applied in GPRS must fit the GSM model.

The GPRS Radio-Block is also 456 bits, as in GSM, and the four GPRS Coding Schemes manipulate the user datato fit this structure. The payload of the Radio-Block includes any higher level protocol overheads, e.g. RLC andTCP/IP headers and these will be examined further on. Table 10 shows how much data can be contained(maximum) within each Radio-Block per Coding Scheme. RLC is the Radio Link Control protocol and has anadditional header that is not included in the figures below.

Table 10 - RLC Data Unit Capacity Per Radio-Block for CS1 to CS4

CS1 CS2 CS3 CS4

Bits 160 240 288 400

Bytes 20 30 36 50

RLC introduces its own overhead, from which the maximum theoretical data rate for each coding scheme is derived.The RLC data unit size plus overhead are divided by 20ms to give this total data rate per timeslot. The effective datarate per timeslot is found by dividing the RLC Data Unit by 20ms. These figures can be found in Table 11.

8. APPENDIX 4 – THROUGHPUT CALCULATIONS



Table 11 - Derivation of Data Rates Per Timeslot for Each Coding Scheme

CS1 CS2 CS3 CS4

RLC Data Unit (bits) 160 240 288 400

RLC Overhead (bits) 21 28 24 28

Total (bits) 181 268 312 428

Data Rate (Kbps) 9.05 13.4 15.6 21.4

Effective Rate (Kbps) 8.00 12.0 14.4 20.0

The Radio-Block is sent in four bursts in exactly the same way as if it were a GSM block containing voice data. APacket Control Unit (PCU) at the Base Station will decide if the data is a GPRS packet, in which case it will be sent tothe SGSN, or a GSM voice call, in which case the call will be routed via the GSM network.

In order to determine how many Radio-Blocks are actually required to transmit a given quantity of data, and toidentify how much of the overall payload is taken up by overhead from intermediate protocols, an example workingfrom the other direction will be considered.

8.3 GPRS Data Coding Example

Suppose 1000 bytes of HTTP or FTP data are to be sent to a GPRS handset. There are several layers of protocolthat need to be added to this payload of data before we get to the radio path. The size of each header is shown inTable 12 and all layers are applied for TCP/IP transmission over PPP.

Table 12 - Protocol Overheads Added to User Data

Protocol Overhead

TCP 24

IP 20

SNDCP 4

LLC 7

Total 55

This means that of our 1000 bytes of data, 1055 bytes need to be incorporated into RLC data units. This determineshow many Radio-Blocks will be needed, rounded up to the nearest whole block.

Table 13 - Number of Radio-Blocks Required for a 1000 Byte Sample of Data

CS1 CS2 CS3 CS4

User Data (bytes) 1000 1000 1000 1000

Total Data (bytes) 1055 1055 1055 1055

RLC Data (bytes) 20 30 36 50

Radio-Blocks Required 53 36 30 22

The maximum average user data rate attainable, assuming Coding Scheme 1 and assuming that we are the onlyuser on the cell for the duration of this transmission, is 7.54 Kbps for this transmission. This is worked out as follows;

The total data rate for CS1 is 9.05Kbps for the whole RLC Data Block (181 bits), of which 160 bits are from the RLCData Unit. Hence, 160 bits divided by 20 ms yields 8.00 Kbps, providing an effective data rate.

The average user data rate is therefore the ratio of how much data the application layer thinks is being transmitted tohow much data is actually being transmitted, multiplied by the effective data rate.



The amount of data actually transmitted is the total payload of all of the Radio-Blocks, even if they are not all fullyutilised. In CS1, the Radio-Block has an effective payload of 20 bytes and when multiplied by the number of blocksrequired yields 1060.

1000 bytesMean User Data Rate = ------------ x 8.00 Kbps = 7.54 Kbps 1060 bytes

It will take a minimum of 0.966 seconds to transmit this data across the air interface. This is obtained by dividing theeffective data rate by the total amount of data.

8.00 Kbps x 1000Minimum Time To Download = ------------------ = 0.966 seconds 1060 bytes x 8

Generically, if D is the amount of data being sent, N is the number of Radio-Blocks required, P is the maximumpayload of the Radio-Block and E is the effective data rate for the Coding Scheme being used then the average userdata rate, R, is determined as follows

D [bytes]R [Kbps] = --------------- x E [Kbps] N x P [bytes]

Where, if O is the overhead introduced by all applicable protocols (55 bytes in this case); D + ON = ------- Rounded up to the nearest whole number. P

The effective data rates for each Coding Scheme can be found in Table 11.

If more than one timeslot is utilised, multiply R by the number of timeslots in use at any given time.

It should be noted that maximum throughput levels are only possible if a device is the only effective user of the GPRScell at that time. If more than one user is transmitting or receiving at the same time, the bandwidth is shared betweenall effective users. However, if the traffic profiles are bursty then there is a reasonable probability that yourtransmission will be in a period when other users are silent.

Finally, if a separate utility is used to monitor the data rate as received by the PC, values much higher than the limitsdescribed here may be observed. This is because the GPRS device has received its Radio-Block over a 20msperiod and buffered it until the whole Radio-Block has been received. The data is then transmitted across the serialor Infrared link at the negotiated speed for that link, which may be significantly higher. For example, 161 bits of datamight be transmitted in 7ms, yielding a brief data rate of 23Kbps. This figure is for example only.



This section details the components of the GPRS network and the interfaces to other networks and services. Theprotocol stacks across the network are also described.

9.1 The GPRS Network

The two key elements in the GPRS network are the SGSN and the GGSN. These form the backbone of the networkand provide the interfaces to other systems, such as the Base Station System (BSS), and external networks, such asthe Internet.

The SGSN is the Serving GPRS Support Node and manages the attaches and contexts of remote GPRS devices.The GGSN is the Gateway GPRS Support Node and provides the access points to external networks. In theVodafone GPRS network the SGSN and GGSN are implemented together as a CGSN (Combined GPRS SupportNode).

Each link in the system is given a label for reference. Um is the air interface, Gb is the GPRS Base Station link, Gnlinks connect the support nodes together and Gi links provide access to external networks such as the Internet.

Figure 4 - The Basic GPRS Network

Figure 4 shows a remote LAN to which connectivity is made. The LAN has its own IP sub-address and everyterminal on that LAN has a unique number within that range, e.g. w.x.y.1, w.x.y.2 and so on.

GPRS enables the roaming user to have a point of presence on that LAN, firewalls etc. permitting. I.e. the GPRShandset will have an IP address with the same sub-address as the fixed terminals on the network, e.g. w.x.y.4.

The Vodafone GPRS Development Environment that has been set up by Vodafone is intended to represent a LANbelonging to the end user and will not be used to provision IP addresses beyond the scope of a test anddemonstration network.

9.2 Protocols in the Transmission Plane

In section 8 a stack of protocols was introduced that are applied to data travelling across the air interface. Additionalprotocols are applied throughout the network to make the data readable by the destination and these are described inFigure 5. Ultimately, the user data must be encapsulated by the correct Layer 2 and PDN protocols so that the datacan be extracted however it is not necessary to apply these protocols across the air interface, thereby conservingbandwidth.

Figure 5 describes the protocols for an end-to-end TCP/IP transmission from the TE all of the way to a terminal onthe destination LAN. The SGSN and GGSN use TCP/IP to communicate with each other and the user data is hiddenwithin this packet using a Gateway Tunnelling Protocol (GTP). This is especially important since the PDP type maynot be IP.

The GGSN is responsible for applying the correct layer 2 (PPP) and layer 3 (IP) protocols so that the fixed terminalhas no direct knowledge that the packet originated on a GPRS network.

9. APPENDIX 5 – GPRS NETWORK ARCHITECTURE

w.x.y.4

BTSSGSN GGSN

Internet

Um

LAN

w.x.y.1

w.x.y.2 w.x.y.3

Address:w.x.y.z

BSC PCU GiGb Gn

BSS CGSN



Figure 5 - GPRS Transmission Plane

PD

N

TC

P

IP

L2 (P

PP

)

L1

Fix

ed IP

Ter

min

alG

GS

N

Rel

ay

GT

P

UD

P/

TC

P

IP L2 L1

L2 L1G

i

SG

SN

Rel

ay

SN

DC

P

LLC

BS

SG

PN

etw

ork

Ser

vice

L1

GT

P

UD

P/

TC

P

IP L2 L1G

n

BS

S

Rel

ay

RLC

/MA

C

GS

M R

F

BS

SG

PN

etw

ork

Ser

vice

L1G

b

ME

Rel

ay

PP

P

L1

SN

DC

P

LLC

RLC

/MA

C

GS

M R

FU

m

TETC

P

IP PP

P

L1

R R

efP

oint

Phy

sica

l Lin

kLo

gica

l Lin

k

an introduction to the vodafone gprs · pdf file1.1 etsi gsm technical specifications ... bss...

Documents